This invention relates generally to ball grid array (BGA) semiconductor packages and more particularly, it relates to an improved method and apparatus for use with a decapsulating machine so as to prevent damage to a fine ball grid array (FBGA) package during decapsulation.
As is generally well-known in the art, with the trend of increased densities in packaging semiconductor chips there has been developed fine ball grid array (FBGA) packages which permit the reduction of the semiconductor packaging profile as well as providing increased package density. Typically, the FBGA packages include a semiconductor die attached to a lead frame mounted on the top surface of a substrate. The semiconductor die is formed with a plurality of bond pads which are electrically connected with the lead frame of the substrate. Further, wire bonds are used to form the connection between the plurality of bond pads on the semiconductor die and terminal pads on the substrate. Conductive elements, such as solder balls, are bonded to conductive traces of the substrate. The semiconductor die, lead frame and wire bonds are encapsulated with a molding compound.
It is often desirable to decapsulate the integrated circuit from the semiconductor packaging after it has been completely fabricated without damaging the lead frame, bonding wires and the like of the integrated circuit. For example, it may be desirable to decapsulate the semiconductor packaging so as to allow for visual inspection of the internal areas thereof, testing and repair of the defective chips therein. Also, it is generally desirable to perform a failure analysis on any defective chips using an emission microscope or microprobing of the chip in order to determine the cause of the failure. The failure analysis is used to enhance reliability and reduce the number of defects in future semiconductor packages.
In the prior art, it is generally known heretofore of various apparatuses and methods for decapsulation of semiconductor packaging. These apparatuses and methods most commonly use hot concentrated acids such as sulfuric acid and nitric acid. One such prior art decapsulator is manufactured and sold by B and G International, Inc. of Soquel, Calif., under their Model 250. An enlarged cross-sectional view of a portion of the decapsulator is illustrated in FIG. 1 of the drawings, showing the primary etchant flow path. FIG. 2 is a view similar to FIG. 1, but shows the secondary etchant flow path.
As can be seen from FIG. 1, the decapsulator 10 includes an acid-resistant gasket 12 which is seated on a quantum etch head 14. A plastic semiconductor or FBGA package 16 to be decapsulated is positioned on top of the gasket 12. A process cover (not shown) is formed with a spring-loaded arm 18 which is used to apply pressure on the semiconductor package 16 when the process is initialized. The semiconductor package 16 and the gasket 12 are sealed and pressurized in a chamber 20 formed by the process cover.
A primary etchant flow (forward path), as indicated by arrows 22-24, produces symmetrically distributed micro-vortex eddy currents in an etch cavity 25 formed by the gasket 12, the semiconductor package 16, and the quantum etch head 14. The eddy currents are propagated outwardly from the etch cavity 25 along arrows 26. The acid is maintained in the etch cavity 25 for a short interval so as to attack the encapsulating material. After the primary etchant flow has been completed, a secondary etchant flow (reverse path), as indicated by arrows 28, 30 and 32 in FIG. 2, produces opposite micro-vortex eddy currents so as to etch the crevices remaining from the forward flow path. After the etching process is finished, the process cover is opened and the semiconductor package 16 is removed.
Unfortunately, various types of deficiencies have been encountered in this prior art B and G encapsulator 10. While not drawn to scale, for this FBGA package 16 the size of the semiconductor die 36 is much larger and the size of the plastic package cover 38 is much thinner than those existing in a conventional dual-in-line (DIP) plastic package. In other words, the die-size to the package-size ratio for the FBGA package 16 is much larger. As a result, this causes the areas 40 to be over-etched by the sulfuric acid during the encapsulation process, thereby damaging the bonding wires and the die in the package. Further, the solder balls 42, as shown in FIG. 2, are susceptible to being damaged or even destroyed due to excessive pressure applied from the spring-loaded arm 18 (FIG. 1).
Therefore, there still exists a need for a novel method and apparatus for use with a decapsulating machine so as to prevent damage to the FBGA package during decapsulation. This is achieved in the present invention by the provision of a fixture assembly of a unique construction struction which includes retaining means for holding and aligning the FBGA package in the decapsulating machine, spacer means for protecting the solder balls on the FBGA package, and cover means for receiving the pressure applied from the spring-loaded arm of the decapsulating machine.
Accordingly, it is a general object of the present invention to provide a novel method and apparatus for use with a decapsulating machine to decapsulate a FBGA package so as to facilitate failure analysis, which has been traditionally unavailable.
It is an object of the present invention to provide a novel method and apparatus for use with a decapsulating machine which permits failure analysis without damaging the FBGA package and the internal components thereof.
It is another object of the present invention to provide an improved method and apparatus for use with a decapsulating machine so as to prevent overetching a FBGA package during decapsulation.
It is still another object of the present invention to provide a fixture assembly for use with a decapsulating machine which includes retaining means for holding and aligning a FBGA package in a decapsulating machine, spacer means for protecting the solder balls on the FBGA package, and cover means for receiving the pressure applied from a spring-loaded arm of the decapsulating machine.
In a preferred embodiment of the present invention, there is provided a fixture assembly for use with a decapsulating machine so as to prevent damage to a FBGA package during decapsulation. The decapsulating machine includes an etch head, an etch-resistant gasket disposed on the top surface of the etch head, and a spring-loaded arm. A retaining gasket has a top surface formed with a recessed aperture and a bottom surface formed with a first central opening. The FBGA package is inserted into the central opening in the bottom surface of the retaining gasket so that the solder balls thereof face upwardly and extend into the recess aperture in the top surface of the retaining gasket.
The retaining gasket with the inserted FBGA package is secured and aligned with the etch-resistant gasket. A spacer element having a second central opening is disposed in alignment with the recessed aperture in the top surface of the retaining gasket so as to create a cavity above the solder balls. An unapertured cover is disposed over the spacer element so as to close the cavity and to receive the pressure applied from the spring-loaded arm of the decapsulating machine during decapsulation.